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Avalanche Forecast

Archived

Apr 16th, 2016–Apr 17th, 2016

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Olympics.

Surface snow could get a better start on being available for loose wet snow avalanches on Sunday. Continue to avoid cornices and areas below where glide avalanches could be a problem.

Detailed Forecast

The upper ridge and warm air mass should further build over the US west coast on Sunday. This should cause light winds and mostly sunny weather in the Olympics and Cascades with further warming temperatures.

Sun and heat effects should be the main factors to consider on Sunday. From a couple of observations it seems like surface snow was probably pretty solidly refrozen in most areas on Saturday morning. But the refreeze may more limited Sunday morning due to warmer weather. If so then surface snow could get a better start on being available for loose wet snow avalanches.

Loose wet avalanches should remain possible Sunday on steeper slopes involving the recent snow. Watch for wet surface snow getting deeper than your boot tops. Triggered loose wet avalanches should be most likely on steep solar slopes but could be seen on any steep aspect in this warm weather. Avoid areas below steep gullies and run out zones that might be prone to natural loose wet avalanches.

The potential for cornice releases may increase through the warm weekend. Cornice releases are basically unpredictable so avoid areas below cornices and remember that cornices can break much further back than expected along ridges.

Although not listed as an avalanche problem, powerful glide avalanches can release unexpectedly so also avoid areas below steep unsupported slopes or rock faces especially if they are showing glide cracks. Glide cracks may be hidden by the recent snowfall.

 

 

Snowpack Discussion

Weather and Snowpack

We've had two big warm-ups and spring shed cycles since the end of March. Over this time period the snowpack has undergone significant settlement with lower elevation snow beginning to fade away and with an overall transition to a spring snowpack.

A front crossed the Northwest Tuesday afternoon and night. Then a cool upper and surface low pressure system moved east along the Washington-Oregon border on Wednesday and Thursday. The NWAC Hurricane site indicated about 4 inches of late season snow ending Thursday morning and no more new snow ending Friday morning.

Storms in March continued to build unusually large cornices along many ridges. The potential for low probability/high consequence encounters, such as cornice failures and glide avalanches from steep unsupported slopes and smooth rock faces, should continue for awhile this spring. 

The mid and lower snowpack in the Olympics should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

NWAC observer Matt Schonwald did a ski trip on Mt Baldy in the Dungeness River drainage in the 3-6800 foot range on Friday 4/15 and generally found 5-15 cm of recent snow over older stable firm snow. No recent or new avalanche activity was seen and small loose wet avalanches only seemed possible on rocky slopes where surface wet snow exceeded a few inches. Some debris was seen from older small loose wet avalanches. There generally wasn't enough snow anymore in the below treeline for avalanches in that area. Matt's partner also turned in a report via Turns All Year.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.